This invention relates to a liquid level gage system useful in determining the level of one or more liquids in a vessel, e.g., a storage tank or the like. More particularly, this invention relates to a liquid level gage system including a displacer which is moved up and down in a vessel to provide signals which can be used to determine the level of one or more liquids in the vessel.
The height or level of a liquid in a storage tank is conventionally determined using a displacer which is secured to a cable and moveable in response to winding or unwinding the cable around or from around a rotatable drum. The drum is coupled to a shaft which is driven, e.g., by a servo motor. Hall effect sensors involving mechanical springs are conventionally used to determine differences in the apparent weight of the displacer as it moves from a liquid phase into a gaseous phase above the liquid phase, or vise versa. Using an optical shaft encoder, one can determine the height of the liquid-gas phase separation.
While such "Hall effect sensor" liquid level gage systems are useful in many situations, they do have certain shortcomings. For example, the accuracy and/or reproducibility of such gage systems is somewhat less than optimum. The mechanical components, in particular the springs, of such gage systems are prone to wear and fatigue, which can cause unreliable or unreproducible liquid level determinations. In addition, in certain situations, it is desirable to determine not only the level of the phase separation between a liquid phase and a gaseous phase, e.g., between a hydrocarbon-rich liquid phase and a gaseous phase, but also between two different liquid phases of relatively similar specific gravities. The "Hall effect sensor" gage systems are not reliable in providing such liquid/liquid phase separation level determination.
Therefore, there exists a need for a new liquid level gage system.